SummaryThe development of the visceral musculature of theDrosophilamidgut encompasses a closely coordinated sequence of migration events of cells from the trunk and caudal visceral mesoderm, respectively, that underlies the formation of the stereotypic orthogonal pattern of circular and longitudinal midgut muscles. Our current study focuses on the last step of migration and morphogenesis of the longitudinal visceral muscle precursors derived from the caudal mesoderm. We show that these

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... eated muscle precursors utilize dynamic filopodial extensions to migrate in dorsal and ventral directions over the forming midgut tube. The establishment of maximal dorsoventral distances from one another and subsequent alignment with their anteroposterior neighbors leads to the equidistant coverage of the midgut with longitudinal muscle fibers. We identify Teyrha-Meyhra (Tey), a tissue-specific nuclear factor related to the RNF220 domain protein family, as a crucial regulator of this process of muscle migration and morphogenesis that is further required for proper differentiation of the longitudinal visceral muscles. In addition, Tey is expressed in a single type of somatic muscle founder cell in each hemisegment. Tey regulates the migration of this founder cell and is required for the proper pathfinding of its developing myotube to specific myotendinous attachment sites.